1. Field
The disclosed and claimed concept relates generally to control circuitry and, more particularly, to an improved control circuit for energizing another device such as a squib.
2. Related Art
As is generally known, a squib is a small explosive device that is employed in various applications. For instance, it may be employed to create special effects in filmmaking, for military uses, and in other applications where it may be necessary to explosively break a safety bolt or other structure in an emergency setting. Other uses for squibs are generally well known.
A particular example of an emergency-related application of a squib is for an explosively activated valve or other component in a nuclear reactor. In such an application, as well as in other applications, a tradeoff always exists between ensuring reliable operation when needed while preventing unintended operations at other times. Known circuits that control the energizing of a squib have typically employed a capacitor which, once charged, is then discharged to energize the squib.
In applications such as the emergency-related applications mentioned above and other applications, the capacitor is typically charged upon the issuance of an ARM command and is then discharged, if appropriate, through the issuance of a FIRE command to employ the charged capacitor to energize the squib. It is desirable in such an application to dissipate within a predetermined period of time the charge stored within the capacitor if the FIRE command is not issued. An example of such a predetermined period of time may be a duration of no more than five minutes. However, it is also desirable that such dissipation of the charge begin only after a predetermined period of time during which the charge will be sufficient to energize the squib, such as a duration of at least thirty seconds.
That is, in such an application it is desirable that the FIRE command is available for a first predetermined period of time after issuance of the ARM command, but that the capacitor is discharged to a safe state of charge within a second predetermined period of time after issuance of the ARM command if the FIRE command is not issued. This is desired in order to avoid the squib being unintentionally energized. Thus, it is desirable that, for at least a first predetermined period of time, the capacitor will remain energized sufficiently to energize the squib, but that after the predetermined period of time the capacitor will become promptly de-energized within another predetermined period of time after arming to place the capacitor in a safe state.
While known circuits have been generally effective for their intended purposes, they have not been without limitation. More particularly, the aforementioned tradeoff between maintaining a charge for a predetermined period of time yet discharging the charge within a subsequent predetermined period of time has been difficult to reliably achieve. It thus would be desirable to provide an improved circuit that enables the maintaining of a charge for a predetermined period of time and also the discharging of the charge within another predetermined period of time.